1. Field of the Invention
The present invention relates to a cleaner-less type image forming apparatus and method (hereafter called a cleaner-less image forming apparatus) that can prevent cleaning efficiency from reducing and maintain high print quality.
2. Description of the Related Art
A transfer roller, a charge brush, and a memory removal brush are made to contact with a photoconductive body in the cleaner-less image forming apparatus adopting a contact transferring method. A sheet of paper is carried with the sheet sandwiched in between the transfer roller and the photoconductive body, and at this time, a toner image formed on the photoconductive body is transferred to the sheet by applying a predetermined bias to the transfer roller.
The charge brush and the memory removal brush are obviously more contaminated or stained as the number of sheets of paper which have been printed grows. For this reason, a transfer bias is preliminarily applied to the transfer roller within an interval which is a period from the time one sheet of paper passes the transfer roller to the time the next sheet reaches the transfer roller, before printing is carried out, in order to clean these brushes.
As the brushes are more contaminated, however, the preliminarily bias voltage that is applied in a usual case cannot fully eliminate the contamination of the brushes. When using a brush charger, it is difficult to keep charge potential on a surface of the photoconductive body uniform, especially due to the toner adhered to the brush, etc. This is because the toner is made up from particles which are insulators, and an electric current between the charge brush and the surface of the photoconductive body is reduced due to the particles adhered to fibers of the charge brush.
Further, the memory removal brush cannot fully disperse the residual toner remaining on the surface of the photoconductive body as a large quantity of toner is adhered to the removal brush, and there is a problem of reducing cleaning efficiency. That is why the image of the previous page appears on the next page, i.e., a so-called memory occurs, and the residual toner on the surface of the photoconductive body is adhered to the sheet of paper, i.e., so-called fog is generated, so that there is a problem of reducing print quality. Additionally, a problem of toner on the backside of a sheet happens such that the residual toner on the surface of the photoconductive body is adhered to the transfer roller, and the toner of the transfer roller is further adhered to the backside of the sheet.